Unless you, dear reader, are a web-scraping software bot quietly pulling this text into a data-hungry LLM, you’re probably a human. And though you’ve likely never seen me in person, you have good reason to believe I’m human, too. But we don’t know one another exist, for sure. In fact, we have no definitive proof that anything is conscious beyond ourselves—a clunkier analogue to René Descartes’ famous dictum: Cogito, ergo sum — “I think, therefore I am.” Forget one another—what if none of it’s real? Not our coworkers, the trees, the constellations—not even ourselves? That’s a question Gizmodo recently posed to a slew of experts across the fields of computer science, philosophy, social psychology, and neuroscience. For this Giz Asks, we asked these experts a straightforward question: How do we know we’re not living in a computer simulation? Their answers—varied and nuanced—offer thought-provoking insights into a question much older than computers themselves, yet one that has remained compelling, if not obsessive, for thinkers through the centuries. With so much technological innovation happening right now, it’s only natural to consider the age-old question with greater scrutiny. We’re creating technology so uncanny, it seems like it will climb out of the valley and dust itself off. Strange, surreal times—the perfect time, I would suggest, to ask how we know what is real at all. Some responses are lightly edited for clarity. For all we know we are, in fact, in a vast computer simulation. Here’s a version of the simulation argument that I am fond of. Suppose that the commonly held view in astrobiology that there is life on other worlds is correct. Further suppose that at least some of these life forms evolve to become technologically sophisticated, developing artificial intelligence to such a degree that they run sophisticated computer simulations. Now, if there are only two civilizations out there that do this, the chances are 2 to 1 that you are in a computer simulation now! Of course, there are many issues with this version of the argument, and those like it, well worth debating. Can consciousness be something that is simulated by a computer? Is it possible to build highly sophisticated AIs, such as quantum computers capable of simulating Earth? Do civilizations survive long enough to develop such technologies, or do they hit some sort of wall or ‘great filter’ in their development. Indeed, perhaps life does not even exist on other planets. (Of course perhaps we are being simulated by future Earthlings, as in the Matrix.) The jury is out, and the issue is a fascinating issue indeed! The hypothesis that we live in a simulation seems provable: it could be the discovery of a flaw in the simulation, such as a distant region of the universe that cannot be zoomed in on, where a telescope would not be able to obtain a clear image. Of course, an even more advanced simulation could roll back time, erase the flaw, and then restart the simulation. This suggests that simulations may vary in type and quality. Nick Bostrom’s Simulation Argument is a brilliant piece of philosophy, suggesting that the initial probability we assign to the idea that we are currently living in a simulation should be revised upward. However, the argument does not convince me, mainly because simulations can be of very different natures. In particular, the Simulation Argument is based on a reference class of simulations created by post-humans, where the simulated beings are nearly indistinguishable from real humans but are unaware of their simulated status. However, it is also conceivable that simulations just as sophisticated could be created, where the simulated beings are aware of their nature. Depending on which of these reference classes is chosen, the conclusion of the argument changes significantly. If the majority of simulations involve beings aware of their simulated nature, it eliminates the disturbing conclusion that we ourselves are simulations, since we are not aware of being simulated. The choice of reference class is therefore crucial. If the argument is based on simulated humans who are unaware of their simulated nature, it leads to the unsettling conclusion that we are likely living in a simulation. Conversely, if the argument focuses on humans who are aware they are being simulated, the conclusion is far more reassuring: we are not such simulations. There is no a priori justification, however, for favoring the choice of humans unaware of their simulated nature over those who are aware of it. Furthermore, one could even argue that simulated humans who are unaware of their nature might be prohibited in a post-human civilization for ethical reasons. One might wonder why the question whether we are in a computer simulation should even be taken seriously. The answer is the simulation argument (which I published back in 2001). The simulation argument shows that at least one of the following propositions is true: (1) the human species is very likely to go extinct before reaching technological maturity; (2) any technologically mature civilization is extremely unlikely to run a significant number of simulations of their evolutionary history (or variations thereof); (3) we are almost certainly living in a computer simulation. To the extent that may think that (1) and (2) are unlikely, therefore, we need to assign substantial probability mass to (3). In any case, the simulation argument reveals an interesting coherence constraint about what one can coherently believe about the future and about our place in the world. The closer we get to reaching the point where human civilization becomes capable of creating ancestors simulations—with conscious minds in it that has experiences of the type that we have—and provided we still retain some inclination to use at least some non-negligible fraction of our resources for that end, the less likely (1) and (2) would appear; and hence the more likely that we ourselves are living in a computer simulation. I think the progress in computer game graphics and in artificial intelligence that we’ve seen over the past couple of decades has made it easier for people to see the simulation hypothesis a plausible view about the nature of existence. Using evidence-based reasoning, we can’t conclusively determine whether we are living in a simulation or not. A sufficiently sophisticated simulation can be totally indistinguishable from reality, and any bugs could always be deleted and then the simulation restarted from before their emergence. There’s also no fundamental barrier to simulating our experiences, especially since one only has to simulate an individual’s perceptions of reality, not the reality itself. Think about how a computer game doesn’t render the whole universe all at once, just the section your located at. A common argument used to claim that we are very likely in a simulation is that there should be far more simulated realities than the singular base reality, thus it’s pretty unlikely we’d happen to be in the base reality. However, this argument is predicated upon the assumption that simulating realities is possible in the first place. Although it’s true that we don’t know of any fundamental objections to doing so, we also don’t know that it is actually possible either! I would tend to give these two possibilities 50:50 odds in the absence of any evidence either way. Another subtly is that if simulated realities can themselves birth simulated realities, then there will be an enormous hierarchy of realities and each one will necessarily have less computational capacity than the ones above it. Eventually one might reason that there will be a lowest level, a sewer of reality, where occupants are simply incapable of building a computer sophisticated enough to ever produce their own convincing simulations. In fact, there should far, far more of these sewer realities than all the others put together and thus we should conclude that’s where we live. This forms somewhat of a contradiction though. We have concluded that we likely live in a reality where simulations are impossible, yet our entire argument is predicated upon the assumption that simulations are possible. These kinds of contradictions deserve more attention and perhaps will eventually help us make sense of this persistent question. Nobody knows whether or not we live in a computer simulation. I put the probability around 20%. I think we might be living in a simulation because I can’t rule out the following premises (one or both may be false, of course, but that is not obvious to me). First, simulation…
